Donald Trump struck back at 2012 GOP presidential nominee Mitt Romney Thursday, blasting the former Massachusetts governor for "begging" for his endorsement four years ago only to sharply criticize him now. "I don't know what happened to him," Trump said during a rally in Portland, Maine. "You can see how loyal he is. He was begging for my endorsement. I could have said, 'Mitt, drop to your knees.' He would have dropped to his knees." "Mitt is indeed a choke artist," Trump said. "He choked like I've never seen anyone choke. Other than Rubio." Trump also said that his net...